John Sayers' Recording Studio Design Forum Archive

Stuart and Dan, thank you very much for your useful information and links.

Stuart, the formaldehyde issue seems important to me as, if I am to make a corner trap, it will be placed next to the heater which may be causing gas release. Do you think i would be fine by placing a foil leaf between the trap and the heater (of course without the heater and the leaf being in touch with each other).

Dan, the link is very helpful. Alphacoustik is a place I was considering calling tomorrow for getting info on their stuff. But I didn't know about the thermo hemp 045. The 16cm looks quite impressive, though I would like to keep the trap at 10cm. Also i dont think thereis a dealer in greece but anyways...

Regardless thank you both for the useful info!
Talk to you soon!

Ok, so after an extensive research on what there is available in my city (or country), regarding effective absorptive material, I ended up at this product http://old.fibran.gr/files4users/files/ ... 051_gr.pdf .

Now, I know that by looking at the GFR rating as well as its density, and by taking in account all the facts about the "GFR/bass absorption" relation that Stuart provided, this product is a definite "no go"!! But if one takes a look at the absorption specs for a second... I don't know but to me it looks quite good for its density, even down to 125hz. In any case, of all the products I have spotted so far available nearby, it is the only one with such great absorption coefficient values at 125 (=0,35) and 250 (0,81), while maintaining a fairly low and even absorption rate at the mids and highs.

So what do you think? Personally I was considering a double leaf (100mm total) for each of the right and left 1st reflection panels, as well as for the SBIR panel between the speakers on the front wall.

As for the corner absorption, I am not sure what to use yet. Maybe the geo_B-040 product that Stuart endorsed previously is better. (http://old.fibran.gr/files4users/files/ ... 040_gr.pdf) . Or do you think that the "b-051" would do a better jod in the corner as well?

Lastly, there are a few knauf dealers nearby that I could consult for purchasing. But there is no absorption graph - or spectrum data anyway - for any of their products that I can spot. It seems awkward to me... Knauf is a serious company as far as I know. But compared to Fibran who are quite detailed on their spec sheet, they are very thrifty! So does anyone know if there is a place in the net where I can find absorption info on their products? So far I have only spotted such info on their perforated products (which is quite impressive I admit!)

So, I was ready to order some rockwool insulation, after having figured out the design for my panels and while talking to the dealer on the phone, she said that it is good to leave a gap of 1-2 cm depth wise, because to her experience the rockwool tends to expand in time (!?!?!). I was surpised to hear that so I asked her if it was some particular product she new that behaved this way and she answered that it occurs with all fiber products. I have never heard of anything like that before!

Stuart (and anyone else), have you ever encountered such a fact, and if yes then would it be enough to leave a 1 cm gap, because the wood depth is exactly 11cm, so I have no space left for more than 1cm . (I am going for the fibran b-051 product which is 150kg/m3 as mentioned before)

the formaldehyde issue seems important to me as, if I am to make a corner trap, it will be placed next to the heater which may be causing gas release. Do you think i would be fine by placing a foil leaf between the trap and the heater (of course without the heater and the leaf being in touch with each other).

I can't say for sure, as I'm not an expert on the subject of gasses emitted by different types of insulation, but I expect that would be OK. I'd suggest that you contact the manufacturer, and ask about that. Explain what you are planning to do, and what your concerns are, then ask them if their product would emit toxic gasses under those circumstances.

taking in account all the facts about the "GFR/bass absorption" relation that Stuart provided, this product is a definite "no go"!! But if one takes a look at the absorption specs for a second... I don't know but to me it looks quite good for its density,

As I mentioned, it's not just the density that matters. There are several other issues involved in the performance of any specific insulation, such as the diameter of the fibers, the average length of the fibers, how they are oriented inside the product, the "tortuosity", they type of binder that is used to hold the fibers together, etc. There's also the issue of HOW it was tested: You'll get very different results from testing it in an impedance tube vs. testing in a reverberant chamber, and testing with A mounting, E-405 mounting, or some the method.

It's not just a simple "density vs. GFR vs. coefficient of absorption" issue. So yes, it is entirely possible that a specific product can show performance that "seems" to defy the rules of thumb.

of all the products I have spotted so far available nearby, it is the only one with such great absorption coefficient values at 125 (=0,35) and 250 (0,81), while maintaining a fairly low and even absorption rate at the mids and highs.

What thickness? A 1" product that has an alpha of 0.35 is pretty good, but a 4" product with an alpha of 0.35 is not great at all! ...

So what do you think? Personally I was considering a double leaf (100mm total) for each of the right and left 1st reflection panels, as well as for the SBIR panel between the speakers on the front wall.

All rooms are different. Whatever product you buy will very likely not react in the exact same way it did in the test laboratory. The only real way to determine if the product will have the effect you want, is to try it out! Do the basic initial testing in the empty room, as I outlined here: http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21122 . Analyze the results. Then put in those panels and repeat the tests. See what changed, and if the results were what you expected / wanted.

When I'm tuning a room, I seldom rely totally on prediction. It is useful, yes, and it can get you "in the ball park" as the Yanks like to say, but I always do multiple tests during the tuning, to make sure that things really are working out the way they are supposed to according to theory... then adjust the plan as necessary. In most cases they do perform roughly as expected, but there's always a need to check and modify.

Lastly, there are a few knauf dealers nearby that I could consult for purchasing. But there is no absorption graph - or spectrum data anyway - for any of their products that I can spot. It seems awkward to me... Knauf is a serious company as far as I know.

Knauf does have some good products, yes. There's an extensive chart of values for many, many products from around the world (including Knauf), on Bob Gold's website. You might find that useful: http://www.bobgolds.com/AbsorptionCoefficients.htm .

she said that it is good to leave a gap of 1-2 cm depth wise, because to her experience the rockwool tends to expand in time (!?!?!).

I've never heard of that happening! It does happen with products that are specifically compressed into packaging for shipping, yes (Eg, Owens Corning SAB) they are very much compressed in the bag, and expand to their correct size when you cut the plastic, but then they don't change dimensions very much. Maybe that's what she was talking about?

Or maybe she was referring to the panels "sagging" over time, as they bend out of shape a little under their own weight? The normal way for dealing with that is to staple some type of thin, light plastic mesh across the frame, just a little bit back from the front edge, to stop it pressing up against the finish fabric.

Like this... That's the back of a panel I have on hand, not the front, but the principle is the same. The mesh is stapled to the frame a little way in, so when the panel is hanging vertically, the insulation can't bulge out, pressing on the finish fabric at the front, nor changing the air gap at the back in this case.

if yes then would it be enough to leave a 1 cm gap, because the wood depth is exactly 11cm,

The gap in this case is about 18mm, but that's NOT because I expect the insulation to expand! It's just to keep it from bending, sagging, or shifting when the panel is in place. In your case you would want that space at the front not the back: just behind the fabric.

- Stuart -

Thanks for taking the time to reply despite being so busy lately! Really appreciate it!
This morning I got the FIBRANgeo b-051 product I was refering to, but after having read your last post, I don't know... I fear I didn't make a very smart choice...
Only way to find out now, as you said, is to build the panels and test it...
I'll also leave the gap on the front side as you proposed.
Thanks for the absorption coefficient chart you linked. Very useful!
Once again, thanks for taking the time to reply!

Ok I'm back. I have constructed the 1st reflection panels as well as the front wall sbir panel, but haven't yet got the spl meter to make precise spl measuring. And since I don't know yet when I will have it in my hands I decided to take a rough measurement to see how the panels perform. And I have to admit... I was totally disappointed. Please check the linked mdat file for details: http://s000.tinyupload.com/index.php?fi ... 4111817791

I used the fibran b051 rock wool ( https://fibran.gr/download/93 ) by placing 2 leaves (10cm total) in each panel. Each panel has roughly 10 - 12 cm air gap on the back. I really can't understand the way it performs. It doesn't make any sense to me... In fact, it seems as though it doesn't make any difference at all. The only thing that has changed sonicaly to my experience is that the imaging is a bit clearer. Despite that nothing seems to have changed realy (apart from the subtle difference in the graphs of course). Edit: Forgot to mention that the Green graph represents the measurement with the panels in place


All I have to say is that it is really frustrating when you can't find the valid materials to use, or when the absorption graphs are misleading. Or maybe there is something I did wrong or don't get right...

I also had concerns about the fabric I used which was not too transparent, though I could still blow air through it while holding it tight against my lips. Bellow you can see a picture of two - of the 3 in total - panels in place (placed with the mirror trick) as well as the fabric's transparency...

https://imgur.com/a/SXBTc46

Any thoughts, Stuart, or anyone else?

I wish Merry Christmas to everyone! God bless!

Where did you put the panels, and how big are they? Those are the key questions. Please post some photos of the room, showing all sides, and also a diagram showing where the panels are, where the speakers are, and where the mix position is.

- Stuart -

Soundman2020 wrote:Where did you put the panels, and how big are they? Those are the key questions. Please post some photos of the room, showing all sides, and also a diagram showing where the panels are, where the speakers are, and where the mix position is.

- Stuart -

OK, after a very long delay time, I'll try to revive this thread, as I am thinking about moving a bit further in treating my room. So, to answer your questions Stuart, I uploaded a sketchup file instead of photos, as I think it will be a lot more useful than just a few photos and a rough handmade sketch. It can be found here: https://files.fm/u/dx6hc5z5
Of course all dimensions of the sketch correspond to the real ones.

The panels placement may be varying slightly than what is shown in the sketchup file, but regardless, they where placed with the "mirror method" at the points where the reflections to the sweet spot were located.

Regarding the dimensions of the panels as seen in the sketchup file they are: 120*60*10 cm (Wood frame is a couple cm thicker than the insulation, thus it is 12cm thick)

So to sum up, the panels didn't work like I was hoping, as seen in the measurements I posted in my previous post about year ago they made very little difference. A couple of weeks ago I had the chance to speak with a good old student mate from university who currently runs his own acoustic consultant company, and though I couldn't show him the measurements he assured me that the density and quality of the material I used shouldn't be a problem since he uses the same company's products in his projects and has been very pleased with them.

But this time I want to take the next step with the treatment and I'll try to describe my plans in short:

1. I am planning to replace the insulation of the sbir panel at least, if not all of them with synthetic polyester one which is way less heavy and provides roughly 0.2 absorption coefficient at 125hz with a thickness of 5cm. To me it looks quite efficient for a product of a density of around 30kg/m3 . I don't have the link right now but I'll post it soon.

2 I am planning to built superchunk style traps in the 2 front corners using mineral wool, but this time I am thinking of following Stuart's proposal of roughly 50kg/m3 or so. I'll be checking the gfr specs first and come here to ask for an extra opinion before purchasing, of course. The problem here is that the right front trap can't be made very deep due to lack of room but it seems I will be able to get it at 30cm wide and around 70cm deep , floor to ceiling (Due to the geometry of the corner it will have to be cuboid style) . Do you think it will be effective enough this way?
Also the left trap will have to be limited to 149cm height only, due to the presence of the bed, as well as the wall cove underneath the ceiling. But regardless I am planing to make this one quite deep. Hopefully 60cm! I think it is the best I could do with this one, what do you think? Would it be effective enough?

3. Regarding the right back corner, I am thinking of filling it with insulation (same as the superchunks), dresser to ceiling, as Stuart proposed in one of his posts a while ago.

4. Last but not least, I am desire to make a ceiling cloud. I would like to use the same polyester material mentioned above, in order to make it as light as possible. From my calculations, the bump I am struggling with around 125 hz must be due to a floor to ceiling axial mode. This material I am planning to use has an absorption coefficient of about 0.2 (5cm thick) at this area of the spectrum as mentioned above, so maybe using 4 pieces of 5cm thick each (20cm total) and leaving a gap of 10cm to ceiling should do the job, right?
And to conclude, by browsing threads around , I admit I got a bit confused about the cloud placement and dimensions:
Should it cover the area vertically right above the speakers, the sweet spot, or the reflection point of speakers to sweet spot? (Probably all the aforementioned but really need help with this).

So that's it for now,
Thanks in advance for any contribution!
I'll probably be coming back with an edit to add more info on the materials I am currently looking at.
Good day to all!

Ok, so I came back to present the materials I am planning to use:

In the bottom of this page you can see the absorption coefficient graph for various of the polyester material I mentioned in my previous post. https://alphacoustic.com/wp-content/upl ... %CE%B1.pdf I am planning to use the one corresponding to the deep blue line. It seems the most efficient in the low mids and is the lightest at the same time. Planning to use at least 10cm thickness - preferably even thicker - for my cloud.
I am also thinking of using this material for a new wider SBIR panel as well as for replacing the insulation of the side first reflection panels, just to make them lighter.

As for the superchunks I am leaning towards the attached file I uploaded in this post. It is not as efficient as I would like it to be as it has an absorption coefficient of 0.22 at 125Hz, but it is the most efficient I can get right now. Other alternative would probably be the Ultracoustic-p from Knauf but I can't find any coefficient graph of it. If anyone ever used it I would love to know how satisfied they might be, and whether it is rigid enough so that it won't sag.

Also, one other thing that concerns me is the fact that I am probably going to end up with extensive absorption in my small room, putting it at the risk of sounding too dead and dull. I'd love to have advise on alternatives to avoid that. Maybe using perforated acoustic boards would do the trick... Any suggestions?

Don't cover up your insulation with fabric yet. Install and measure before/after installation. If you need to increase your decay time at higher frequencies, you can do things such as adding strips of plastic under the fabric or slats of wood under/over top of the fabric. Also perforated panels over your bass traps would help. Again, until you see your REW measurements, it's hard to determine exactly what you should do. You will want to install the slats/plastic above or below ear height to prevent any first reflections.

Greg

Gregwor wrote:Don't cover up your insulation with fabric yet. Install and measure before/after installation. If you need to increase your decay time at higher frequencies, you can do things such as adding strips of plastic under the fabric or slats of wood under/over top of the fabric. Also perforated panels over your bass traps would help. Again, until you see your REW measurements, it's hard to determine exactly what you should do. You will want to install the slats/plastic above or below ear height to prevent any first reflections.

Greg

Thanks a lot for the useful tips, Greg!
In fact I was indeed planning to measure before covering the insulation. I was also aware of the use of slats / perforated panels for compensating with the high frequency decay time, but I had no idea of what to get and how to install them. That said, I was unaware of the "above/below ear placement" which is a very very useful tip indeed, which makes great sense when I think about it... Thanks!!

But there is more to be done before I get to that.

My main concern right now as mentioned before regards the design / size and placement of the Corner absorbers as well as the type of insulation to be used. The "fibran b040" I linked previously has a density of 40kg/m3 which corresponds to Stuart's recommendations, but its GFR is 15000 MKS Rayls which is more than double of what Stuart recommends...

There is also the alternative of getting the "fibran b030" which has a density of 30 kg/m3 but a GFR of 10000 MKS Rayls. But the problem is that Fibran doesn't include any graph of absorption coefficient across the spectrum for this particular product in its leaflet.

On the other hand there is the alternative of getting a knauf product instead, ie. the ultracoustic-p which has a GFR of 5000 MKS Rayls, but there is no density mentioned and it doesn't look rigid at all so I am afraid it will sag easily. I am so confused... I really wish I could get Roxul/Rockwool Safe n' Sound where I live, but I can't...

And speaking of sagging, what could I do to prevent it? Is there any link I could follow for construction of corner trap? The first reflection panels I made consist of 150kg/m3 insulation so I didn't have to think about sagging at all. But at significantly lower densities with panels stacking one above the other it would be an issue, right?

My main concern right now as mentioned before regards the design / size and placement of the Corner absorbers as well as the type of insulation to be used. The "fibran b040" I linked previously has a density of 40kg/m3 which corresponds to Stuart's recommendations, but its GFR is 15000 MKS Rayls which is more than double of what Stuart recommends...

There is also the alternative of getting the "fibran b030" which has a density of 30 kg/m3 but a GFR of 10000 MKS Rayls. But the problem is that Fibran doesn't include any graph of absorption coefficient across the spectrum for this particular product in its leaflet.

On the other hand there is the alternative of getting a knauf product instead, ie. the ultracoustic-p which has a GFR of 5000 MKS Rayls, but there is no density mentioned and it doesn't look rigid at all so I am afraid it will sag easily. I am so confused... I really wish I could get Roxul/Rockwool Safe n' Sound where I live, but I can't...

If you go to:

http://www.acousticmodelling.com/porous.php

Punch in some numbers in there to see the difference.

Here is a screenshot I took after entering some values from your post. You can see the improvement in low frequency absorption with increased GFR. Note, mks rayls/m is equivalent to Pa.s/m2

And speaking of sagging, what could I do to prevent it?

For broadband panels hanging off of the ceiling, I've done a few things. One way is to staple string across the face (under the fabric of course) to hold up the insulation. The other thing I've done is screw in some 1x2 across the face. Both seem to work fine. The string method would be better in terms of having less hard surfaces to reflect the sound.

For super chunks, you could just put in a divider panel or two depending on how soft the insulation is. Splitting up the stack with dividers will prevent the insulation from compressing due to the weight of the insulation above it.

Greg

If you play around with the numbers more, you'll notice that lower GFR performs better at lower frequencies when it's thicker: Greg

musictracer wrote:The other thing I've done is screw in some 1x2 across the face

I guess you mean some sort of slat, and the dimensions correspond to cm, right?

I played a bit with the calculator you linked and it seems quite handy.
Only that, I am not sure how truly it corresponds to reality, as there are many other factors that play a role to acoustical performance. And I am saying this because the fibran b051 insulation I used for my panels have a GFR of 120000 MKS Rayls (!!!!) which, according to its leaflet performs way better than what the calculator shows. In fact the company states that it is suitable for acoustic panels construction... (something that in my case didn't seem to work to be honest.)

Regardless, the calculator seems to give a decent rough approximation of what to expect. Many thanks for mentioning!

So, according to the calculator, the knauf ultracoustic-p (5000 MKS Rayls) seems to be performing best for my corner traps. It will probably sag more easily compared to the fibran product, but I guess I will manage to prevent this thanks to your recommendations.

Other than that, I have contacted Knauf to ask about its density and a few other info, since I will need to calculate the weight of the corner traps before I build the frame. I only hope they will respond...

I will report back as soon as I get that info.

I guess you mean some sort of slat, and the dimensions correspond to cm, right?

I don't have any pictures sadly, but say I built the rectangular frame out of 1x6 dimensional lumber. That means it's real life dimensions are 3/4" x 5.5". So, if I put in 4" thick insulation, that would leave 1.5". I put a 1x2 on both ends and one in the middle -- all "on edge". A 1x2 in real life dimensions is 3/4" x 1.5". So, the 1.5" of the 1x2 filled in the remaining 1.5" gap left over from the insulation not fully filling the framing. I hope that makes sense. If it doesn't, let me know and I'll try to do a quick SketchUp for you.

Greg